The present invention relates to industrial roofing, such as low slope roof diaphragms (Panelized Roof Systems) that are generally flat. Panelized Roof Systems can be installed over large or small warehouses. In these systems, roof sheathing comprises plywood or oriented strand board decking panels (generally 4 foot by 8 foot) with stiffeners pre-framed at 16 or 24 inches on center. The long dimension of each decking panel typically is oriented parallel to a support. Adjacent panel edges are placed over and nailed to common framing members. The roof forms a blocked diaphragm, which has significantly greater seismic and high wind resistance than conventionally framed roofs with unblocked sheathing. Various low slope roof diaphragm configurations are shown in the Engineered Wood Association publication “Lateral Load Connections for Low-Slope Roof Diaphragms”, APA The Engineered Wood Association (2004).
Metal (usually galvanized steel) tie-straps are nailed over the roof decking (or sheathing) panels to transfer tension forces between two framing members. This creates a tension/compression connection from the wall to the inner portion of the diaphragm. This combination then is covered with built up roofing membrane usually comprising layers of felt, strapping, roofing tar and roofing shingles or rolls.
Typical roofing materials such as asphalt and modified bitumen and gravel can absorb more than seventy percent (70%) of the solar energy that falls upon them. Roofs having dark roofing materials, which tend to absorb more radiant or solar energy, may become as hot as 88° C. (190° F.) on a sunny day. Moreover, it has been reported that urban areas, such as Los Angeles, Calif., can record temperatures about 3 to 4° C. (6 to 8° F.) hotter than surrounding areas. These urban heat islands (i.e., differences in temperature between urban and rural areas) result in increased air-conditioning costs, energy use and pollution. (http://www.professionalroofing.net/past/oct98/feature.asp).
Metal tie straps (or continuity ties) are now required by building codes to be installed as support for roof regions of low-slope roofs near building side walls. In some cases the tie straps are installed onto decking panels throughout the roof diaphragm. Such metal tie straps conduct heat energy and cause the regions where such straps are found to become hotter than adjoining roof regions. Such excessive heating leads to “hot spots” where the asphalt and bitumen roof structure is even hotter than neighboring roof regions. These “hot spots” weaken the roof membrane, accelerate aging of the roof, and require additional maintenance to avoid leaks that can cause structural failure if not repaired in a timely manner. The industry continues to seek a panelized roof system that does not create “hot spots”.